This application is based on Application No. 2000-327225, filed in Japan on Oct. 26, 2000, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to an electromagnetic device such as a stepping motor, a solenoid valve, or the like, used in an automotive continuously variable transmission, for example.
2. Description of the Related Art
FIG. 6 is an external view of a permanent-magnet stepping motor, FIG. 7 is a cross section taken along line VIIxe2x80x94VII in FIG. 6, FIG. 8 is a cross section taken along line VIIIxe2x80x94VIII in FIG. 7, FIG. 9 is a cross section taken along line IXxe2x80x94IX in FIG. 7, and FIG. 10 is a partial exploded perspective of the stepping motor in FIG. 7.
In the figures, a permanent-magnet (PM) stepping motor 1, which is immersed and used in an oil, includes: an outer casing 2 made of a resin; a tubular housing 12 made of a resin which is linked to the outer casing 2; a motor main body 3 disposed inside the outer casing 2; a shaft 4 functioning as a moveable shaft rotated by the motor main body 3; and a conversion mechanism 31 for converting rotation of the shaft 4 into rectilinear motion. Moreover, the outer casing 2 and the housing 12 constitute a cover.
The motor main body 3 includes a stator 5 secured to the outer casing 2, and a rotor 6 secured to the shaft 4. The stator 5 has: coils 7 each constructed by winding a conducting wire in which an electrically-insulating layer is formed on a copper wire surface; coil terminals 8 led out from the coils 7; connector terminals 9 connected to the coil terminals 8; and an outside connector 25 connected to the connector terminals 9. The rotor 6 has a bush 10 secured to the shaft 4, and a circumferentially-magnetized hollow cylindrical permanent magnet 11 fitted over and secured to the bush 10.
The housing 12 is fastened to the outer casing 2 by a plurality of screws 12A extending parallel to the shaft 4. A circular interfitting aperture 2a is formed in the outer casing 2, and an interfitting portion 12a for inserting into the interfitting aperture 2a is formed on the housing 12. As shown in FIG. 8, three positioning projections 12b, which protrude radially and come into contact with an inner circumferential surface of the interfitting aperture 2a, are formed on an outer circumferential surface of the interfitting portion 12a. Furthermore, an annular groove 12c is formed in a joining surface of the housing 12, where the housing 12 joins the outer casing 2.
A housing communicating aperture 12d communicating between internal and external portions of the housing 12 is disposed in a side surface portion of the housing 12. A filter 13 for catching contaminants contained in the oil is disposed in the housing communicating aperture 12d. The shaft 4 is rotatably held by a casing bearing 14 and a housing bearing 15. The housing bearing 15, which is secured inside the housing 12, is a rubber-seal type.
A rod 16 reciprocated in an axial direction of the shaft 4 by rotation of the shaft 4 is disposed at a tip portion of the housing 12. A base-end portion of the rod 16 is inserted inside the housing 12, and a tip portion of the rod 16 protrudes from the tip portion of the housing 12. A rod communicating aperture 16a communicating between the internal portion of the housing 12 and an internal portion of the rod 16 is formed in the rod 16. A sleeve 17 for guiding rectilinear motion of the rod 16, an oil seal 18 for preventing penetration of contaminants from an outer circumferential portion of the rod 16, and a ring-shaped stopper 19 for regulating progression of the rod 16 are each secured to an inner circumferential surface of the tip portion of the housing 12.
The conversion mechanism 31 includes a thread portion 4a, a guide member 20 made of a resin which is formed in the base-end portion of the rod 16 and is engaged with the thread portion 4a, and a stopper 21 made of a metal which is secured to the shaft 4 and regulates regression of the rod 16. Stopper surfaces 20b and 21a which are perpendicular to the direction of rotation of the shaft 4 are formed on the guide member 20 and the stopper 21, respectively. As shown in FIG. 9, a rotation-regulating projection portion 20a which protrudes radially and regulates rotation of the rod 16 is formed on an outer circumferential portion of the guide member 20. Consequently, the guide member 20 is displaced in an axial direction of the shaft 4 by rotation of the shaft 4. An operating member 22 made of a resin is mounted to the tip portion of the rod 16.
A construction of the stator 5 will now be explained in detail with reference to FIGS. 11 to 16.
As shown in FIG. 11, conducting wires 50 constituting the coils 7 are each formed by coating an electrically-insulating layer 52 onto a copper wire 51. As shown in FIG. 12, the coils 7 are each constructed by winding the conducting wires 50 for a predetermined number of winds into a bifilar winding (parallel winding) on a conducting-wire spool portion 53a of first and second bobbins 53A and 53B. In other words, the coils 7 are constructed by winding first and second conducting wires 50A and 50B onto each of the conducting-wire spool portions 53a together side by side in an annular shape. Then, as shown in FIGS. 13 and 14, first to third coil terminals 8A, 8B, and 8C are mounted to each of the first and second bobbins 53A and 53B, the electrically-insulating layer 52 is removed from a winding start end of the first conducting wire 50A and the winding start end of the first conducting wire 50A is wound onto a tie-off portion 8a of the first coil terminal 8A and soldered, the electrically-insulating layer 52 is removed from a winding finish end of the second conducting wire 50B and the winding finish end of the second conducting wire 50B is wound onto the tie-off portion 8a of the third coil terminal 8C and soldered, and in addition, the electrically-insulating layer 52 is removed from a winding finish end of the conducting wire 50A and a winding start end of the conducting wire 50B and the winding finish end of the first conducting wire 50A and the winding start end of the second conducting wire 50B are both wound onto the tie-off portion 8a of the second coil terminal 8B and soldered.
As shown in FIG. 15, the coils 7 wound onto the first and second bobbins 53A and 53B are embedded in an outer molding 54. Here, each of the coil terminals 8A, 8B, and 8C is folded and bent, and the tie-off portions 8a to which the end portions of the conducting wires 50A and 50B are soldered are also embedded in the outer molding 54. In addition, as shown in FIG. 16, cores 55 made of iron are disposed so as to surround the coils 7, completing the construction of the stator 5.
In the stepping motor 1 constructed in this manner, as shown in FIG. 17, the coils 7 are constituted by first phase and second phase excitation coils 7a and 7b connected in series, and third phase and fourth phase excitation coils 7c and 7d connected in series. A connection portion M1 connecting the first phase and the second phase excitation coils 7a and 7b, and a connection portion M2 connecting the third phase and the fourth phase excitation coils 7c and 7d are grounded, a voltage of +14 V being applied between a terminal S1 of the first phase excitation coil 7a and the connection portion M1, a voltage of xe2x88x9214 V being applied between the connection portion M1 and the terminal S2 of the second phase excitation coil 7b, a voltage of +14 V being applied between a terminal S3 of the third phase excitation coil 7c and the connection portion M2, and a voltage of xe2x88x9214 V being applied between the connection portion M2 and a terminal S4 of the fourth phase excitation coil 7d. Moreover, the first conducting wire 50A and the second conducting wire 50B wound onto the first bobbin 53A correspond to the first phase and the second phase excitation coils 7a and 7b, respectively, and the first conducting wire 50A and the second conducting wire 50B wound onto the second bobbin 53B correspond to the third phase and the fourth phase excitation coils 7c and 7d, respectively.
This stepping motor 1 is mounted to an automotive continuously variable transmission, for example, and the operating member 22 attached to the tip portion of the rod 16 is engaged with a link 40 which opens and closes a transmission control valve in the continuously variable transmission.
When electric power is supplied to the coil 7 through the external connector 25, the first phase to fourth phase excitation coils 7a to 7d are magnetized, rotating the rotor 6 and the shaft 4 together. The guide member 20 is engaged in the thread portion 4a on the shaft 4, and since rotation of the guide member 20 is regulated, rotation of the shaft 4 is converted into rectilinear motion of the guide member 20 and the rod 16.
The transmission control valve is opened and closed by means of the link 40 by reciprocation of the rod 16, ultimately changing the rotational velocity ratio between the drive shaft and the engine shaft.
The conventional stepping motor 1 is mounted to an automobile continuously variable transmission, for example, and is entirely immersed in the oil, which contains sulfur and organosulfur compounds. Then, the electrically-insulating layer 52 is removed from the end portions of the conducting wires 50A and 50B, and the end portions of the conducting wires 50A and 50B are wound onto the tie-off portions 8a of the coil terminals 8A, 8B, and 8C and soldered. Thus, the sulfur and organosulfur compounds in the oil permeate the outer molding 54, reaching the soldered portions of the conducting wires 50A and SOB. Because the electrically-insulating layer 52 is removed from the end portions of the conducting wires 50A and 50B and the end portions of the conducting wires 50A and 50B are wound onto the tie-off portions 8a in a single layer and soldered as shown in FIG. 18, the amount of solder 56 in the soldered portions is small. For that reason, the sulfur and the organosulfur compounds react chemically with the solder 56 in the soldered portion, corroding the solder 56. Thus, one problem has been that the sulfur and organosulfur compounds reach the copper wire 51 due to the corrosion of the solder 56, and the copper wire 51 reacts chemically with the sulfur and organosulfur compounds and corrodes, eventually causing the conducting wires 50A and 50B to break. Or because the amount of solder 56 is small, the copper wire 51 of the conducting wires 50A and 50B is not completely embedded in the solder 56, exposing a portion of the copper wire 51, and therefore another problem has been that direct chemical reactions occur between the exposed copper wire 51 and the sulfur and organosulfur compounds, corroding the copper wire 51 and causing the conducting wires 50A and 50B to break.
The sulfur and organosulfur compounds in the oil permeate the first and second bobbins 53A and 53B and the outer molding 54, and in addition permeate the electrically-insulating layer 52, reaching the copper wire 51. Then, chemical reactions occur at the surface of the copper wire 51 and organosulfur compounds are formed on the surface of the copper wire 51, giving rise to a state of decreased adhesive strength of the electrically-insulating layer 52 to the copper wire 51. In this state, damage arises in the electrically-insulating layer 52 due to interference between adjacent conducting wires 50A and 50B caused by repeated thermal expansion and thermal contraction due to the heat history of the conducting wires 50A and 50B themselves.
In the conventional example, because the coil 7 is constructed by winding the conducting wires 50A and 50B onto the conducting-wire spool portions 53a of the first and the second bobbins 53A and 53B in a bifilar winding (parallel winding), the conducting wires 50A and 50B, which have large electric potential differences, are wound side by side. Thus, yet another problem has been that when damage arises in the electrically-insulating layer 52, the chemical reactions between the copper wire 51 and the sulfur and organosulfur compounds are promoted due to the large electric potential differences between the conducting wires 50A and 50B, causing the copper wire 51 to corrode and break.
The present invention aims to solve the above problems and an object of the present invention is to provide an electromagnetic device in which wire-breakage tolerance of a conducting wire is improved.
In order to achieve the above object, according to one aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including:
an outer casing;
a moveable shaft supported by the outer casing;
a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and
a coil embedded in an outer molding, the coil being constructed by winding onto the bobbin a conducting wire in which an electrically-insulating layer is coated onto a copper wire,
wherein the electrically-insulating layer is removed from an end portion of the conducting wire and the end portion of the conducting wire is wound onto a tie-off portion of a coil terminal mounted to the bobbin to constitute a wound-on portion,
a solder-retaining member is mounted so as to cover the wound-on portion of the conducting wire on the tie-off portion, and
the wound-on portion of the conducting wire is soldered to the tie-off portion together with the solder-retaining member.
The solder-retaining member may be a cylindrical shape disposed so as to surround the wound-on portion of the conducting wire.
The solder-retaining member may be composed of a solder-plated steel plate.
The solder-retaining member may be a conductor wire wound so as to overlap the wound-on portion of the conducting wire.
The conductor wire may be a solder-plated copper wire.
The end portion of the conducting wire from which the electrically-insulating layer is removed may be wound onto the tie-off portion in multiple layers.
According to another aspect of the present invention, there is provided an electromotive device used in an oil, the electromagnetic device including:
an outer casing;
a moveable shaft supported by the outer casing;
a bobbin disposed inside the outer casing so as to be disposed around the moveable shaft on a common axis with the moveable shaft; and
a coil embedded in an outer molding, the coil being constructed by winding onto the bobbin a conducting wire in which an electrically-insulating layer is coated onto a copper wire,
wherein the bobbin is constituted by first and second bobbins arranged in an axial direction of the moveable shaft, and
the coil is constituted by first phase and second phase excitation coils formed by winding two strands of the conducting wire into unifilar windings on a conducting-wire spool portion of the first bobbin, and third phase and fourth phase excitation coils formed by winding two strands of the conducting wire into unifilar windings on a conducting-wire spool portion of the second bobbin.
The first phase excitation coil may be constructed by winding one strand of the conducting wire for a predetermined number of winds onto a bottom-surface side of the conducting-wire spool portion of the first bobbin, the second phase excitation coil may be constructed by winding the other strand of the conducting wire for a predetermined number of winds onto the conducting-wire spool portion of the first bobbin so as to overlap the first phase excitation coil, the third phase excitation coil may be constructed by winding one strand of the conducting wire for a predetermined number of winds onto a bottom-surface side of the conducting-wire spool portion of the second bobbin, and the fourth phase excitation coil may be constructed by winding the other strand of the conducting wire for a predetermined number of winds onto the conducting-wire spool portion of the second bobbin so as to overlap the third phase excitation coil.
The conducting-wire spool portions of the first and second bobbins may be each divided into two divided spool portions in an axial direction of the moveable shaft, and the first phase to fourth phase excitation coils may be constructed by winding one strand of the conducting wire onto each of the divided spool portions of the conducting-wire spool portions of the first and second bobbins.